Insulation Resistance Measurement Circuit for Ungrounded Power Systems
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Solution Overview
Problem
In ungrounded power supply systems, existing insulation monitoring devices require costly galvanic isolation for signal interfaces, leading to signal loops and measurement errors due to the absence of a direct ground connection, which complicates coupling and increases costs.
Innovation Solution
A circuit arrangement with an active measuring voltage is implemented, where the ground connection of the signal evaluation circuit is set at ground potential, eliminating the need for galvanic isolation by preventing interference currents and allowing direct coupling of insulation monitoring devices without measurement errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If galvanic isolation is implemented for signal interfaces in insulation monitoring devices, then signal distortion and measurement errors are prevented, but device complexity and cost increase significantly
Solution Approach 1:
The patent introduces an intermediary potential transformation stage that converts all signal levels to a common reference potential before further processing. This mediator eliminates the need for galvanic isolation by providing a stable reference point that prevents signal distortion without requiring complex isolated interfaces for each signal path.
Solution Approach 2:
The patent merges all potential differences into a single transformation stage at the input of the signal evaluation circuit. By combining all potential transformations at one location rather than requiring isolation at each interface, the system achieves measurement accuracy without the complexity of multiple isolated interfaces.
2Reliability
If galvanic isolation is implemented for each signal interface, then coupling between insulation monitoring devices is achieved, but cost increases due to required relays and data couplers
Solution Approach 1:
The patent creates a universal potential reference system that serves all signal interfaces simultaneously. This single reference potential system provides coupling reliability for all devices without requiring individual isolation components (relays, data couplers) at each interface, significantly reducing manufacturing cost while maintaining reliability.
3Reliability
If the ground connection of the signal evaluation circuit is not connected to earth potential, then galvanic isolation is maintained, but signal loops and interference currents occur
Solution Approach 1:
The patent establishes equipotentiality by connecting the ground connection of the signal evaluation circuit to a defined potential (earth potential or potential of an active conductor). This creates a stable reference that eliminates potential gradients and prevents interference currents while maintaining the necessary galvanic isolation through the single transformation stage.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution reduces costs by eliminating the need for galvanic isolation, prevents signal loops, and enables accurate insulation resistance and impedance measurements in ungrounded power supply systems, even in multi-pole configurations, while allowing for the detection of line breaks and unintentional connections between power supply networks.
Implementation Method 1
A measuring voltage generated by the measuring voltage generator actively drives a measuring current via the active conductor(s) and through the insulation resistance back into the measuring path
Implementation Method 2
The voltage drop measured across the measuring resistor is fed via a signal input to a signal evaluation circuit for evaluation to determine the insulation resistance
Data Source
Figure 1
Figure 2
Figure 3a~3b
AI summary
The invention relates to a circuit arrangement (20) with an active measuring voltage (UG) for determining an insulation resistance (RF) or a complex-valued insulation impedance (IF) of an ungrounded power supply system (12) against earth potential (PE), with a measuring path (24) running between an active conductor (L1, L2) of the power supply system (12) and the earth potential (PE), which has a measuring voltage generator (VG) for generating the measuring voltage (UG), a measuring resistor (RM) for tapping a measured voltage (UM) and a coupling resistor (RA), and with a signal evaluation circuit (26) which has a signal input for evaluating the measured voltage (UM) and a ground connection (GND), wherein the ground connection (GND) is connected to the earth potential (PE).